我坚持升级 Kubuntu 16.04。它开始升级，然后停止一段时间并给出错误 503。我尝试从 repo 手动下载文件，但尽管目录中存在文件，但我无法下载它们。apt-get clean并且apt-get upgrade --fix-missing也没有解决这个问题。我该如何解决这个错误？
$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
wine-staging wine-staging-amd64 wine-staging-i386:i386 winehq-staging
4 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 51.2 MB/54.0 MB of archives.
After this operation, 1064 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Err:1 …